Polyethylene glycol (PEG) compounds contain a polyether unit, commonly expressed as R1-(O-CH2-CH2)n-O-R2. They are generally biocompatible, non-toxic and stable in both organic and aqueous solutions, and so are extensively used in biological applications, as well as nanotechnology and materials research. Proteins with PEG chain modifications and compounds encapsulated in PEG liposomes exhibit a longer half-life in vivo than their non-PEGylated counterparts, a phenomenon known as PEG shielding. Functionalised PEG lipids and phospholipids can be used for protein-PEG conjugation. 4-Arm PEG-Alkyne is a multiarm PEG derivative with alkyne or acetylene groups at each terminal of the four arms connected to one pentaerythritol core. PEG alkyne can used for PEGylation via a copper-catalyzed click chemistry reaction with azide.